i dont know the exact time but in recent memory:
super robot taisen Original Generations 2 - 2 complete playthroughs to see all the branching paths and unlock all the secrets
Super Robot Taisen Judgement - just finished my first playthrough and for similar reasons as OG2 i will playing through the game a total of 4 times then i will get to Super Robot Taisen W for DS. SRT J clocks in at 52 chapters >_>
Valyrie Profile 2 - dual playthroughs + multiple seraphic hate completions to get angel slayer.
Radiata Stories - all characters recruited in my book.
Star Ocean 3 - tried to get all battle trophies but gave up after i unlocked sound test
Rouge Galaxy - unlocking all constumes takes some serious time :o